224 E. A. Schäfer, 



Here again the lines of junction between the sarcous elements 

 and the clear intervals which separate them from the membranes of 

 Krause are obscured by these optical effects of the transverse networks 

 and membranes: unless the length of the clear intervals is sufficient 

 to remove the line of junction beyond the bright stria 1 ). When this 

 is the case, and in mammalian muscle it is not unfrequent, the junction 

 of sarcous element and clear interval becomes visible as a straight, 

 sharply defined line, whereas in insect muscle the borders of the 

 bright stria are ill defined and often have a scolloped appearance 

 (Fig. 1). 



As with the wing-muscles, so in the ordinary muscles, the actual 

 structural conditions of the muscle-segments, which are obscured in the 

 living muscles by the reflexion and refraction effects which the 

 membranes and networks produce upon the light, come out very 

 clearly in the alcohol-fixed muscles and especially in those which are 

 afterwards stained by gold after the method recommended by Rollett. 

 Here the distinction between the sarcous elements, which are stained, 

 and the clear intervals, which remain perfectly colourless, is most 

 striking. As in the wing -muscles also, the length of the clear 

 intervals varies with the condition of extension of the fibre. In 

 extended fibres it is considerable (Figs. 40, 41, 44) and the clear un- 

 stained bands may be as long as the dark, stained bands or may 

 even exceed them in length; in retracted parts it is proportionally 

 less, so that only a narrow interval may intervene between the 



represent the transverse networks) when the microscope focus is superficial. Now 

 add vinegar and allow it to act freely upon the fibre. The double rows of dots 

 become very distinct and have the same appearance in the deep as in the super- 

 ficial focus: the membranes of Krause are seen as fine transverse lines passing 

 across the muscle columns betwen the muscle segments; the stria of Amici, that is 

 to say a line composed of well marked dots, is no longer seen in any focus 

 (Fig. 24 B). 



*) The term „bright stria" is here used to distinguish the appearance seen in 

 living muscle from the „clear band" or „clear interval" which is visible in the 

 alcohol muscle: the distinction of term being intended to denote that though corre- 

 sponding generally in situation the appearances are partly due to different causes. 

 Thus the „bright stria" may be coterminous with the clear interval, or it may fall 

 short of the extent of the latter, or, on the other hand, as is especially the case in 

 contracted muscle, it may extend far beyond it. 



